In the processing of a substrate, e.g., a semiconductor substrate or a glass panel such as one used in flat panel display manufacturing, plasma is often employed. As part of the processing of the substrate in a plasma chamber, the substrate is for example processed in a series of steps in which materials are selectively removed (etched) and deposited in order to form electrical components thereon.
In an example chamber implementation based on an Exelan™ plasma processing system platform (available from Lam Research Corporation of Fremont, Calif.), RF energy is employed to ignite and sustain the plasma within the intended plasma sustaining region, i.e., the region within the plasma processing chamber where plasma presence is intended for substrate processing purposes. During plasma processing, the return RF current may be conducted away from the plasma sustaining region via, for example, the upper electrode. The RF return current travels, in this example implementation, outside a confinement ring area across a chamber ceiling and a chamber liner traversing RF straps and a lower ground bucket back to an inner surface of a cantilever bore. Along this complicated path, the return RF current traverses several interfaces that join adjacent RF chamber components (or members).
As is typically the case for machined components, many of the RF chamber components have mating surfaces, interfaces, gaps or sharp edges due to machining or tolerance considerations. These sharp corners and surfaces themselves form gaps when adjacent RF chamber components are mated together, presenting high-impedance obstacles to the RF current.
Without wishing to be bound by theory, it is believed that in some cases, the high-impedance may cause a high voltage to be built up across a gap. If the voltage is built up sufficiently high, a spark or arc may result across the gap. Such arcing may, in many cases, cause charged particles such as electrons or ions to be ejected into the surrounding gas space(s). The gas space(s) surrounding many of these RF chamber components, while not disposed in the plasma generating region that is intended for generating and sustaining plasma during processing, may nevertheless be in a condition conducive to igniting and/or sustaining plasma during chamber operation. Accordingly, the unintended injection of charged particles may lead to the unwanted ignition of plasma in the gas space(s) surrounding these gaps even though these gas space(s) are not in the aforementioned intended plasma generating region (e.g., the region generally defined by the upper electrode, the lower electrode, and the surrounding confinement rings).
When one of these unwanted ignition events occurs, the plasma chamber is said to be suffering a plasma un-confinement event, which is a highly undesirable condition for the substrate processing environment, for the substrate currently being processed, and may lead to damage to chamber hardware components, particularly to the electrostatic chuck.
It should be noted that different RF chambers may have different components and or designs, and the RF current may take different paths in different chambers. Irrespective of the particulars of the different RF chambers, the RF current in many chambers tend to traverse multiple RF chamber components and tend to sporadically suffer from similar gap-related arcing and unwanted plasma ignition problems.